Based on Ulster Presbyterian immigrant correspondence and recent research in Irish religious demography, this essay argues that Unionist cultural and political hegemony over northern Irish Protestants was constructed largely because of the massive emigrations (mostly to the United States) of Ulster Presbyterians, between the 1790s and the 1850s, who would or could not accommodate themselves to the political and socioeconomic regime fastened on the north of Ireland after the United Irishmen's failed rebellion of 1798 and the Act of Union in 1800. Hence this essay directly challenges revisionist scholars who argue that Ulster Presbyterians' post-1798 embrace of the Union and the Orange Order was rapid, inevitable, and natural.